Individualising anti-cancer treatment: Optimising tracking accuracy and dose delivery in Stereotactic Body Radiotherapy (SBRT)
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Introduction:
Stereotactic Body Radiotherapy (SBRT) is a form of highly focal radiation therapy. Treatment delivery
is largely guided (“tracked”) by gold-marker fiducials for non-spinal body sites. CyberKnife (CK) is
purpose-built todeliver SBRT.
Methods:
An experimental system, using a radiotherapy “phantom”, was designed to assess the accuracy of the
CK system in imaging static and migrating fiducials (Chapter 2). An assumption in fiducial-tracked
treatments is that the exact arrangement of fiducials at planning CT is maintained at treatment. It is
also crucial that relative Organ At Risk (OAR) and tumour position, is consistent between planning CT
scan and treatment. The validity of this assumption was assessed by comparing fiducial locations on
Planning and Treatment CTs (Chapter 3). The feasibility of achieving consistent bladder filling, and
the impact of consistent filling on the ability to track translations/rotations in prostate cancer
therapy was explored (Chapter 4). Uncertainties in treatment planning/delivery for CK prostate
patients was explored, and ideal planning margins were calculated (Chapter 5). Optimum SBRT dose
for localised pancreatic cancer, lymph node oligometastasis and oligometastatic breast cancer was
explored (Chapter 6).
Results:
Imaging of fiducial position was accurate and reproducible across a clinically appropriate tracking
range. However, findings highlighted the need for vigilance at treatment delivery. The reliability and
“trackability” of implanted fiducials, as well as consistency of OAR position, varied according to
tumour and implantation site. Guidelines were generated accordingly. Bladder filling/Margins
guidelines have been generated. Radiobiological analysis has indicated that there is scope for
cautious dose escalation in the SBRT treatment of pancreatic cancer. Analysis of SBRT-treated lymph
node oligometastases has demonstrated that Local Control is 100% when SBRT is prescribed to a
threshold 72Gy10.
Conclusion:
Refinements in patient preparation, fiducial placement, and dose/fractionation selection can
optimise tracking accuracy and dose delivery in SBRT.
Authors
Goldsmith, Christy SaronCollections
- Theses [3834]